1. Field of the Invention
The present invention relates to a position deviation detecting method for use in an image forming device which forms a multi-color or color image, and relates to an image forming device using the position deviation detecting method.
2. Description of the Related Art
As for the color image forming device, it is important to eliminate the color deviation between the output images of the magenta, the cyan, the yellow and the black on the transfer medium, for the purpose of upgrading the image quality. Especially, the elimination of the color deviation is important in the four-drum tandem type color image forming device which is equipped with the set of the image supporting medium and the optical writing unit for each of the colors respectively. In this image forming device, the images of the different colors are formed through the optical writing units and the image supporting mediums, and the color deviation may take place due to the deviation of the transferring position when the image of each color is transferred one by one to the printing material with the intermediate transfer medium or the transfer medium. Thus, the elimination of the color deviation is the important problem.
There has been proposed the method of compensating the color deviation due to the deviation of the transferring position. In the proposed method, the pattern for position deviation detection is optically written to the image supporting medium, and the resulting latent image pattern is developed with the corresponding toner. After the development, the pattern of toner image is transferred to the intermediate transfer medium or the transfer medium, the pattern transferred to the intermediate transfer medium or the transfer medium is optically read by the pattern detection sensor which includes the light emitting device and the photodetector. Thereby, the amount of position deviation is detected by the pattern detection sensor, and the compensation of the color deviation is carried out in accordance with the writing timing or using the optical system compensation unit.
See Japanese Patent No. 3518825 (corresponding to Japanese Laid-Open Patent Application No. 09-244341), Japanese Patent No. 3266849 (corresponding to Japanese Laid-Open Patent Application No. 11-272037), and Japanese Patent No. 3353629 (corresponding to Japanese Laid-Open Patent Application No. 09-234905).
FIG. 10 shows an example of the pattern according to the related art when detecting the amount of position deviation in the main scanning direction between two of the plurality of colors.
The plurality of the patterns 1 and 2 of different colors are provided for detecting the amount of position deviation in the main scanning direction as shown in FIG. 10. These patterns are arranged in the vertical posture along the reading direction of the pattern detection sensor. The pattern detection sensor includes the light emitting device and the photo detector. As described above, the amount of position deviation in the main scanning direction is detected based on the respective outputs of the sensor when reading the detection patterns.
According to this method, the patterns 1 are made in the color with high sensor sensitivity (any of the magenta, the cyan, and the yellow) and the patterns 2 are made in the color with low sensor sensitivity (the black). The patterns 1 and 2 are arranged so that the patterns 2 of the color with low sensor sensitivity is set in the fixed position in the main scanning direction as the reference patterns, and the patterns 1 of the color with high sensor sensitivity are shifted relative to the patterns 2 and some of the patterns 1 are overlapped over the patterns 2 in the fixed position.
In the above method, the patterns 1 and the patterns 2 are arranged in the above manner, and the amount of position deviation in the main scanning direction is measured. However, when the patterns 1 of the color with high sensor sensitivity greatly deviate from the patterns 2 in the fixed position, some of the patterns 1 are completely separated from the sensor sensitivity region as shown in FIG. 11, and it is difficult to attain the detection of the exact amount of position deviation.
Moreover, FIG. 12 shows an example of the deviation detection patterns according to the related art when detecting the amount of position deviation in the sub-scanning direction between two of the plurality of colors.
The plurality of sets of the patterns 1 and 2 of different colors are provided for detecting the amount of position deviation in the sub-scanning direction as shown in FIG. 12. These patterns are arranged in the horizontal posture along the reading direction of the pattern detection sensor. The pattern detection sensor includes the light emitting device and the photo detector. As described above, the amount of position deviation in the sub-canning direction is detected based on the respective outputs of the sensor when reading the deviation detection patterns.
According to this method, the first interval at which the patterns 1 of the color with high sensor sensitivity are arranged is shifted slightly on the basis of the second interval at which the patterns 2 of the color with low sensor sensitivity are arranged as the reference patterns such that the first interval is smaller than the second interval. The overlapping amount of the pattern 1 and the pattern 2 of each set varies according to the reading direction of the sensor, the plurality of patches are formed with the sets of the patterns 1 and 2.
However, when the patterns 1 and the patterns 2 are arranged by this method to detect the amount of position deviation in the sub-scanning direction, the sensor sensitivity region in the neighborhood of the reference patch where the patterns 1 and 2 of the two colors completely match each other is affected by the outputs of the sensor from the patterns 1 of the color with high sensor sensitivity of the two patches adjacent to the reference patch, and it is difficult to attain the detection of the exact amount of position deviation.